Yes, although it depends on what the circuit is supposed to do. If a guitar FX box you will just get slightly different FX. If a hi-fi preamp you will get a bit less gain and a lot more distortion. 12AX7 like a high resistance in the anode circuit, which means either high HT/B+ or an active load.

Yes, although it depends on what the circuit is supposed to do. If a guitar FX box you will just get slightly different FX. If a hi-fi preamp you will get a bit less gain and a lot more distortion. 12AX7 like a high resistance in the anode circuit, which means either high HT/B+ or an active load.

Thank you for your quick reply. would the changes be in the power supply or in the amplifier circuit?